Casting process and mould

ABSTRACT

A process for casting a piston for an internal combustion engine including tilting, the mould portions which define the casting cavity through at least 45 degrees about a horizontal axis after filling and before solidification in such a manner that the axis of rotation of the component moves in the direction of the vertical. A casting mould for casting a piston for an internal combustion engine includes mould portions which define the casting cavity that are tiltable through at least 45 degrees about a horizontal axis after filling and before solidification in such a manner that the axis of rotation of the piston moves in the direction of the vertical.

FIELD OF THE INVENTION

The invention relates to a method for casting a piston for an internal combustion engine and a corresponding casting tool.

Both horizontal and vertical casting methods are known for rotationally symmetrical components such as pistons for internal combustion engines. In the horizontal casting method, the axis of rotation of the component to be cast is aligned so as to be substantially horizontal. This method is currently mainly used in the manufacture of diesel pistons, the majority of which are cast with inserts, such as, for example, ring carriers and salt cores for the later cooling channel. It is largely the vertical casting method that is used for casting pistons for gasoline engines, the majority of which do not have cast inserts.

STATE OF THE ART

For vertical casting methods, machines which allow casting at a tilt of up to 30 degrees from the vertical position are known as examples of prior use.

A casting method is revealed by DE 10 2006 058 145 A1 in which the material is introduced according to the principle of bottom casting and is solidified according to the principle of top casting. CH 135526 A relates to a method and a mold for casting composite blocks, in which the angular position of the mold is changed during casting.

DESCRIPTION OF THE INVENTION

The invention is based on the object of providing a casting method, and a corresponding tool, which method is improved over the known methods, and also on the object of combining at least some of the advantages of both the horizontal casting method and the vertical casting method.

This object is achieved on the one hand by the method described in claim 1.

According to this claim, the tool portions defining the casting cavity are rotated or tilted, after the filling of the casting cavity or at least toward the end of this process and before solidification, by at least 45 degrees about a horizontal axis such that the axis of rotation of the piston to be cast moves in the direction of the vertical position and preferably at least draws near thereto. The fundamental idea of the invention is therefore essentially to fill the casting cavity in a substantially “horizontal” position of the casting cavity. This offers particularly advantageous filling conditions since comparably thin regions such as, for example, the remaining wall thickness between the later cooling channel of a piston and a ring carrier can be better filled than with vertical casting. Moreover, when filling in the horizontal state, foreign particles representing imperfections in the cast component, such as oxides or alfin deposits, are advantageously guided into regions of the workpiece and can later be removed with minimal effort or have to be processed and therefore removed in any case.

The invention makes use of the advantages of vertical casting in that the feeding action is better here. This is essentially due to the fact that a substantially rotationally symmetrical component is cast, the casting cavity of which is filled via a feeder on one side with the horizontal casting method. During the tilt in the direction toward the vertical casting method as according to the invention, the more advantageous, substantially symmetrical feeding action of a central feeder is used. In particular, it is expected that owing to the improved feeding the porosity in the cast component will be reduced.

According to the invention it is important that the casting cavity is tipped in its entirety such that the alignment of the axis of rotation of the component to be cast changes, as described. The apparatuses and methods known in the state of the art, in which individual tool portions which abut the casting cavity but do not define this as a whole can be swiveled, are therefore not comparable with the method according to the invention.

Taken as a whole, the tool can be described as a cavity mold.

Advantageous embodiments of the method according to the invention are described in the further claims.

In order to be able to influence the behavior of the material to be filled in or already filled in the casting cavity in an advantageous and particularly precise manner, it is preferred that the tilting movement, or in other words the position of the axis of rotation of the component during filling, and/or the tilting angle and/or the position of the axis of rotation of the component during solidification can be set. By means of flexibly setting the tilting angle, the filling behavior and/or the solidification behavior can be advantageously and individually influenced.

In order to be able to make use of the advantages and the existing experience with horizontal casting methods in a particularly comprehensive manner, it is presently preferred that the axis of rotation of the piston to be cast is aligned during filling so as to be substantially horizontal.

For the same reasons, it is advantageous if the axis of rotation of the piston to be cast is aligned during solidification so as to be substantially vertical.

For filling the casting cavity it is preferred, in order to make use of the advantages of horizontal casting methods, that the liquid material is filled into a lateral region of the piston to be cast. In order words, a sprue is located in a lateral region and preferably approximately in the lower third of the casting cavity to be filled with a horizontal casting method.

With respect to the casting tool according to the invention, it is advantageous if the mold cavity has at least one recess which, with horizontal casting methods, is located in an upper region, preferably at the highest region, of the mold cavity. In this way, a kind of dirt pocket forms in this region once the filling is complete, into which any impurities are washed.

The benefits of the vertical casting method can be taken advantage of in a particularly comprehensive manner by a feeder being disposed in an upper region, in particular in a different place from the sprue, after the tilting of the casting cavity.

As indicated above, the advantages of the method according to the invention are particularly realized when the component to be cast is cast with at least one insert such as, for example, a ring carrier and/or a core for a cooling channel of a piston for an internal combustion engine. Even though it is easier, and is therefore a preferred option, to put in inserts when the component to be cast is aligned so as to be horizontal, it is preferred for certain applications that inserts are put in with the vertical casting method and that the tool is subsequently tilted, and with the horizontal casting method that the mold cavity is filled.

The aforementioned object is also achieved by means of the casting tool described in claim 8, with which the method previously described and the advantages thereof are implemented using an apparatus. The preferred embodiments of the casting tool according to the invention substantially correspond to those of the preferred method described above. Moreover, it should be mentioned that the individual features of all of the methods described herein can be applied to the apparatus and vice versa.

BRIEF DESCRIPTION OF THE DRAWING

The drawing schematically shows the method according to the invention when casting a piston for an internal combustion engine.

DETAILED DESCRIPTION OF ONE EMBODIMENT OF THE INVENTION

As can be seen from the drawing, the procedure according to the invention is described with the help of the positively shown piston 10 for an internal combustion engine which is to be cast, but it is clear that the casting cavity which receives the later piston is at first empty and is defined and enclosed by suitable tool portions that are not shown. As shown in the drawing, the axis of rotation A of the piston to be produced is in its initial state, i.e. for the filling of the mold cavity it is aligned so as to be substantially horizontal. The piston pin bore 12 can be seen approximately in the center of the piston. Furthermore, for the example shown, a feeder 16 is provided in the end region which is at the top after the tilting (cf. the right-hand part of the drawing). During the filling, the feeder is located on one side of the workpiece, but after the filling, and for the solidification of the workpiece, it is located at the highest point of the workpiece. A sprue is designated by 14 in the drawing, which is located to the side during the filling of the casting cavity, according to the representation in the drawing “in front of” the mold cavity. The sprue 14 is preferably provided in a different position from that of the feeder 16 and is preferably provided so as to be separate therefrom. At the highest point of the mold cavity during casting, a recess 18 is preferably provided in the mold cavity, which forms a kind of dirt pocket into which impurities are washed. These can easily be removed with the subsequent processing. The recess 18 can be provided anywhere along the axis of rotation A of the piston 10.

The symmetry of the piston 10 to be produced during the solidification process is utilized in that the mold cavity defining the later piston, as shown in the right-hand region of the drawing, is tilted after the molten material is filled in such that the axis of rotation of the component to be produced is aligned so as to be substantially vertical. In the embodiment shown, in this state the feeder 16 is located in an upper region. In this alignment it can be expected that the solidification conditions will lead to advantageous properties of the component produced. For example, owing to the filling in a horizontal position, foreign particles such as oxides and alfin deposits are to be found in an edge region of the piston, where they can easily be removed, and not, as is to be expected when filling in a vertical position, in the bottom region of the piston. This bottom region can therefore be provided with the method according to the invention as a finished cast bottom region with corresponding contours which does not have to be further processed. 

1. method for casting a piston for an internal combustion engine, in which the tool portions defining the casting cavity are tilted after filling and before solidification by at least 45 degrees about a horizontal axis such that the axis of rotation of the component moves in the direction of the vertical position.
 2. The method according to claim 1, wherein a tilting angle can be set.
 3. The method according to claim 1 wherein the axis of rotation of the piston is aligned so as to be substantially horizontal during filling.
 4. The method according to claim 1, wherein the axis of rotation of the piston is aligned so as to be substantially vertical during solidification.
 5. The method according to claim 1, wherein the casting material is filled into a lateral region of the piston.
 6. The method according to claim 1, wherein after the tilting of the tool portions a feeder is disposed in an upper region of the piston.
 7. The method according to claim 1, wherein at least one insert, such as, for example, a core for a cooling channel and/or a ring carrier, is cast into the piston.
 8. A casting tool for casting a piston for an internal combustion engine, in which the tool portions defining the casting cavity are tiltable after filling and before solidification by at least 45 degrees about a horizontal axis such that the axis of rotation of the piston moves in the direction of the vertical position.
 9. The casting tool according to claim 8, wherein a tilting angle can be set.
 10. The casting tool according to claim 8 wherein a feeder is disposed in a region lying along the axis of rotation of the piston at the end of the piston.
 11. The casting tool according to claim 8, wherein the tool portions defining the casting cavity can be tilted such that after the tilting a feeder is disposed in an upper region.
 12. The casting tool according to claim 8, wherein the mold cavity has at least one recess which, when the axis of rotation of the piston to be cast is aligned so as to be horizontal, is located in an upper region, preferably at one of the highest points. 